1. Field of the Invention
This invention relates generally to mixing and more particularly to a method of mixing and apparatus therefor having a novel, three-dimensional mixing motion with a non-repetitive mixing pattern which is especially adapted for applications requiring fine, non-destructive mixing.
2. Description of the Prior Art
Mixing devices are presently employed in a wide variety of fields including the pharmaceutical, drug, chemical and food industries, for example. Many of the applications in these industries require non-destructive mixing in which dry or semi-moist solid materials are mixed in a manner which will not destroy or impair the individual physical properties of the materials being mixed. If conventional mixers of the type having beaters rotating at high speeds are employed, the materials being mixed are often ground and beaten to the point where they lose their original properties. In the food industry, for example, non-destructive mixing applications arise when relatively fragile foods or ingredients, such as shelled nuts, for example, must be mixed with other substances in a manner which will not grind the nuts or reduce them to small fragments.
Other problems arising in the mixing of materials include generation of heat and thoroughness of the mixing action. When high speed mixers are employed to increase the efficiency of the mixer and produce a more thorough mixing action, the materials being mixed are often raised in temperature because of the high speed working and movement of the materials. In many fields of use, such as the fine chemical and pharmaceutical industries, for example, a substantial rise in temperature of the materials being mixed could have a deleterious effect on the chemical and physical properties of the materials and, consequently, resort is often had to expensive cooling systems for the mixing bowls which keep the temperature of the mixed materials within prescribed limits. When a slower mixing speed is utilized, the temperature problems are minimized but the desired small temperature rise is often obtained at the expense of the thoroughness of the mixing action. For this reason, mixing apparatus having a large number of mixing arms and other appendages which follow complicated mixing patterns have been developed. Needless to say, this type of mixer is not only expensive to manufacture but is also expensive and time consuming to maintain. A suitable mixer for fine mixing and other industrial applications should also exhibit low vibration and noise characteristics, be suitable for use with mixing bowls of different shapes, and be usable with partially-filled mixing bowls as well as filled mixing bowls.